Overbased detergents are well described to provide lubricating properties. Often such detergent additives are proportioned with other lubricating additives to provide lubricating oil compositions that exhibit certain desired lubricating properties.
Alkaline-earth metal hydroxybenzoates are also known as additives for engine lubricating oils.
U.S. Pat. No. 5,895,777 describes lubricating oil additives comprising the alkaline-earth metal salts of aromatic carboxylic hydroxy acids containing carboxylic acids having 16 to 36 carbon atoms.
European Patent Application No. 1,154,012 describes lubricating compositions comprising an oil, an anti-wear additive and a sole oil-soluble overbased detergent comprising an aromatic carboxylate, such as a calcium salicylate substituted by a hydrocarbon remainder.
British Patent No. 1,146,925 describes lubricating compositions comprising, as lubricating agents, polyvalent metal salts, in particular calcium, and alkylsalicylic acids comprising more than 12, preferably 14 to 18 carbon atoms in the alkyl group. These salts can be prepared from the corresponding sodium salts, as synthesis intermediates.
British Patent No. 786,167 describes polyvalent metal salts of oil-soluble organic acids, such as sulfonic hydrocarbons, naphthenic acids or alkylhydroxybenzoic acids, in particular alkylsalicylic acids having an alkyl radical of up to 22 carbon atoms. The alkylsalicylic acids can be prepared from sodium alkylsalicylic acids according to the processes described in British Patents Nos. 734,598; 734,622 and 738,359. The sodium alkylsalicylates described in these British patents are useful as synthetic intermediates for the preparation of alkaline-earth alkylsalicylates, which are also useful as additives for lubricating oil.
In general, the above references describe processes for aromatic hydroxy carboxylic acids and their salts which are derived from alkaline salts of phenol derivatives, such as phenol itself, cresols, mono- and dialkylphenols, the alkyl group having from about 8 to 18 carbon atoms, halogenated phenols, aminophenols, nitrophenols, 1-naphthol, 2-naphthol, halogenated naphthols, and the like. The processes described above, however, lead to products having high sediment content at high TBN that decrease product yield and create added disposal expense. Thus, it is desirable to have a process that improves product yield by minimizing the sediment resulting from such processes.